1. Field of the Invention
The present invention relates to an explosive cartridge for use in an explosive column train, the cartridge being especially adapted for a two component explosive composition.
2. Description of the Prior Art
One prior art method of placing an explosive composition into a borehole is by use of a plurality of explosive containing cartridges placed in end to end relationship to form a columnar explosive train. The usual method of coupling the cartridges one to another is to provide the nose and tail end of each cartridge with male and female threads, respectively, and to screw the cartridges together. Such an arrangement is shown in U.S. Pat. No. 3,246,602, Meredith et al. In this patent, the tail end of each cartridge is provided with a closure member inserted into a tapered throat section at the rear of the cartridge. As one cartridge is screwed into engagement with another, the nose end of the rear cartridge wedges the closure member tightly into the throat section to form a watertight seal, so that water in the borehole will not be able to enter the cartridge and desensitize the explosive.
However, when a two component field mixed explosive is used in an explosive train, particular problems are encountered. Quite commonly, in two component field mixed explosives, there is a first solid component, made up of granules of nitrate or perchlorate compounds, and a second liquid component which is generally an organic sensitizer or a chemically activating liquid. Such explosive compositions are easily desensitized by water. Also, when the liquid component is added to the solid component, there is generally a substantial "slump" (i.e. a reduction in volume of the solid component, which can be up to as high as 25% of the initial volume, depending upon the composition and the granule size of the solid component). Such slump can be minimized by using a finer grain size of the solid oxidizer, but this in turn inhibits field mixing of the two components. When the several cartridges are joined in end to end relationship, this slump must be taken up in a manner to eliminate an air gap between the explosive charges of the several cartridges, to ensure detonation throughout the entire explosive column. The use of light flexible cartridges which can take up slump simply by deforming to a smaller volume has not been entirely satisfactory since the packages are sometimes too weak to resist puncture when slid into a borehole. On the other hand, the cartridges known to the applicants herein which are made of a harder, more puncture resistant material have not adequately solved the problem of mantaining a proper seal between the cartridges, while permitting allowance for such slump to ensure adequate proximity of the explosive charges of the several cartridges.
Thus, it is an object of the present invention to provide an effective explosive cartridge especially adapted for use in an explosive column train, where a field mix, two component explosive composition is used.